• The Journal of Engineering Geology
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• v.24 no.1
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• pp.69-79
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• 2014

This study aims to elucidate the relative importance of geological characteristics, soil slope, and rainfall intensity in relation to soil erosion. To this end, indoor rainfall simulation experiments were carried out under different conditions of rainfall intensities, soil slope, and geological characteristics. The test results show that the factors affect soil erosion in the order of soil slope > rainfall intensity > organic content in the soil. Erosion rates were proportional to rainfall, and increase with increasing clay content. Therefore, the soil erosion rate increases strongly with increasing organic content and clay content. The results show that the soil erosion rate in areas of metamorphic rocks shows a marked increase compared with areas of steep slope and sedimentary rocks. These results indicate that the geological characteristics to produce soil are closely related to sedimentation before and after erosion, providing basic information for the development of models to predict soil erosion rates.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.3 no.1
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• pp.38-44
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• 1991

A simple box model was applied to the sedimentation of fine-grained sediments in a rectangular basin. Using the model explanation of the net depositional process of One-grained sediments in a small tide-dominated rocky embayment was possible by a careful evaluation of coefficients for erosion and deposition. For a basin with an inlet through which the exchange of suspended sediments occurs between open sea. the model shows that the time-averaged concentration of suspended sediments for a tidal cycle reaches a steady state initial abrupt change in concentration. During a tidal cycle deposition of sediments seems to occur when the magnitude of tidal currents is substantially low near the slack waters. Resuspension and erosion of bottom sediments take place near the peak of tidal currents. For a depositional basin. Gamagyang Bay, the duration and the maximum rate of deposition appear to be longer and higher than those of erosion. which accounts for the net deposition of fine-grained sediments. The time-averaged concentration of suspended sediment in the basin is slightly lower than that of the open water due to the net deposition. The instantaneous concentration of suspended sediments showed the maximum value about an hour before high water and the minimum about an hour after low water.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.1 no.1
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• pp.44-49
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• 1989

Cohesive sedimentation mechanism is affected by various physico-chemical factors. Thus, the field observations and the laboratory experiments for cohesive sediment have been reported for decades. Erosion and deposition test was carried out with cohesive sediment material sampled in the Keum River Estuary in this study. The change of the suspended cohesive sediment concentration was measured for various flow conditions, which have the purpose to determine the critical shear stress and the coefficients for erosion and deposition . The critical shear stress and the coefficient for erosion were determined in the flume test. The equilibrium concentration was determined for each shear stress and the relationship between the normalized equilibrium cocentration with the initial cocentration (Ceq/co) and the equivalent shear stress was obtained. The experimental results were compared with the other results and showed fairly well agreements with them.

• Journal of the Korean GEO-environmental Society
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• v.18 no.1
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• pp.37-47
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• 2017

The Mekong River plays an extremely important role in Southeast Asia. Flowing through six countries, including China, Myanmar, Thailand, Laos PDR, Cambodia, and Vietnam, it is a site of great biological and ecological diversity and the habitat of numerous species of fish. It also supports a very large population that lives along the river basin. Therefore, much attention has been focused on the giant Mekong River Basin, particularly, its soil erosion and sedimentation problems. In fact, many methods have been used to calculate and simulate these problems. However, in the case of the Mekong River Basin, the available data is limited because of the extreme size of the area (about $795,000km^2$) and lack of equipment systems in the countries through which the Mekong River flows. In this study, we applied the Universal Soil Loss Equation (USLE) model in a GIS (Geographic Information System) framework to calculate the amount of soil erosion and sediment load during the selected period, from 1951 to 2007. The result points out dangerous areas, such as the Upper Mekong River Basin and 3S Basin (containing the Sekong, Sesan, and Srepok Rivers) that are suffering the serious consequences of soil erosion problems. Moreover, the present model is also useful for supporting river basin management in the implementation of sustainable management practices in the Mekong River Basin and other basins.

• Proceedings of the Korea Contents Association Conference
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• 2006.11a
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• pp.413-416
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• 2006

This paper presents a strategic approach to effective soil conservation planning and management. To do this, the soil loss model, Revised Universal Soil Loss Equation (RUSLE) was used to quantify soil erosion in two basins (Andong and Imha basin), which are distinct in terms of sedimentation in the reservoir of each basin. Areas with high soil erosion potential were analyzed on the basis of land surface characteristics handled by geographic information system (GIS), especially dividing the basin into several sub-basins and then examination was emphasized near the river channel (water-pollutant buffering zone), along which human activities are large. Modeling results show the approach suggested herein provides a basis and guideline for choosing prior erosion risk areas to be examined for soil conservation planning and management. Also, this approach is relatively simple and has wide practical applicability.

• Journal of the Korean Society of Safety
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• v.32 no.4
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• pp.46-52
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• 2017

Sediment exchange in river has been affected by artificial changes such as dredging and abnormal climate changes like intense rainfall. Over last decades in Korea, there were many constructions, restoration or rehabilitation in rivers. Therefore, deposition and erosion become more actively occurred than before, which may threaten the river safety such as flood defense. For safety's sake, the dredging of river bed, which is considered as the most typical measure, has been increased to extend hydraulic conveyance compared with previous conditions. However, since it might change the sediment mechanism, there would be another risk at which unexpected side effects such as headward erosion could be occurred. Particularly, sedimentation at abrupt expansion region is able to lead to hydraulic characteristics like water elevation in the upstream region in the beginning of dredging, which, however, has been barely studied in this field. Therefore in this study, the relationship between sediment mechanism at dredging section and hydraulic characteristics in upstream region were presented through numerical simulations in the idealized abruptly widen channel using Delft3D. The ideal channel of 2,000 m length with each side angle of 45 degrees at abruptly widen expansion region was employed to consider the sediment angle of repose. The sensitivity analysis was performed on the dimensionless factors consisted of upstream and downstream depths($h_u$, $h_d$), width($w_u$, $w_d$), water level(H), flow rate(Q) and discharge of sediment($Q_s$). And the sedimentation amount at dredging and the upstream hydraulic characteristics were investigated through that analysis. It showed that $h_d/h_u$, $H/h_u$ and $w_d/w_u$ were more influential in sequence of effect on sedimentation amount, while $h_d/h_u$, $w_d/w_u$ and $H/h_u$ on upstream region. It means that $h_d/h_u$ was revealed as the most significant factors on sedimentation, also it would most highly affect the rising of water level upstream.

• Magazine of the Korean Society of Agricultural Engineers
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• v.22 no.4
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• pp.108-114
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• 1980

A deterministic conceptual erosion model which simulates detachment, entrainment, transport and deposition of eroded soil particles by rainfall impact and flowing water is presented. Both upland and channel phases of sediment yield are incorporated into the erosion model. The algorithms for the soil erosion and sedimentation processes including land and crop management effects are taken from the literature and then solved using a digital computer. The erosion model is used in conjunction with the modified Kentucky Watershed Model which simulates the hydrologic characteristics from watershed data. The two models are linked together by using the appropriate computer code. Calibrations for both the watershed and erosion model parameters are made by comparing the simulated results with actual field measurements in the Four Mile Creek watershed near Traer, Iowa using 1976 and 1977 water year data. Two water years, 1970 and 1978 are used as test years for model verification. There is good agreement between the mean daily simulated and recorded streamflow and between the simulated and recorded suspended sediment load except few partial differences. The following conclusions were drawn from the results after testing the watershed and erosion model. 1. The watershed and erosion model is a deterministic lumped parameter model, and is capable of simulating the daily mean streamflow and suspended sediment load within a 20 percent error, when the correct watershed and erosion parameters are supplied. 2. It is found that soil erosion is sensitive to errors in simulation of occurrence and intensity of precipitation and of overland flow. Therefore, representative precipitation data and a watershed model which provides an accurate simulation of soil moisture and resulting overland flow are essential for the accurate simulation of soil erosion and subsequent sediment transport prediction. 3. Erroneous prediction of snowmelt in terms of time and magnitute in conjunction with The frozen ground could be the reason for the poor simulation of streamflow as well as sediment yield in the snowmelt period. More elaborate and accurate snowmelt submodels will greatly improve accuracy. 4. Poor simulation results can be attributed to deficiencies in erosion model and to errors in the observed data such as the recorded daily streamflow and the sediment concentration. 5. Crop management and tillage operations are two major factors that have a great effect on soil erosion simulation. The erosion model attempts to evaluate the impact of crop management and tillage effects on sediment production. These effects on sediment yield appear to be somewhat equivalent to the effect of overland flow. 6. Application and testing of the watershed and erosion model on watersheds in a variety of regions with different soils and meteorological characteristics may be recommended to verify its general applicability and to detact the deficiencies of the model. Futhermore, by further modification and expansion with additional data, the watershed and erosion model developed through this study can be used as a planning tool for watershed management and for solving agricultural non-point pollution problems.

• Proceedings of the Korea Water Resources Association Conference
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• 2002.05a
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• pp.3-16
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• 2002

This article describes some of the recent and on-going research developments of the author at Colorado State University. Advances in the field of sedimentation and river mechanics include basic research and computer modeling on several topics. Only a few selected topics are considered here: (1) analytical determination of velocity profiles, shear stress and sediment concentration profiles in smooth open channels; (2) experiments on bedload particle velocity in smooth and rough channels; (3) field measurements of sediment transport by size fractions in curved flumes. In terms of computer modeling, significant advances have been achieved in: (1) flashflood simulation with raster-based GIOS and radar precipitation data; and (2) physically-based computer modeling of sediment transport at the watershed scale with CASC2D-SED. Field applications, measurements and analysis of hydraulic geometry and sediment transport has been applied to: (1) gravel-bed transport measurements in a cobble-bed stream at Little Granite Creek, Wyoming; (2) sand and gravel transport by size fraction in the sharp meander bends of Fall River, Colorado; (3) changes in sand dune geometry and resistance to flow during major floods of the Rhine River in the Netherlands; (4) changes in hydraulic geometry of the Rio Grande downstream of Cochiti Dam, New Mexico; and (5) analysis of the influence of water temperature and the Coriolis force on flow velocity and sediment transport of the Lower Mississippi River in Louisiana. Recent developments also include two textbooks on "Erosion and Sedimentation" and "River Mechanics" by the author and state-of-the-art papers in the ASCE Journal of Hydraulic Engineering.

• Journal of Wetlands Research
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• v.16 no.2
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• pp.221-233
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• 2014

Soil erosion, transportation, and sedimentation by water flow often occur in a stream. This excessive occurrence threatens the safety of hydraulic structures, and aggravates natural disasters like flood. To prevent soil disaster according to the soil erosion, it is necessary to predict accurate sediment outflow primarily. Besides, it is very important to choose appropriate models by basin characteristics, to estimate accurate quantity of related factors, and to acquire available hydrological data. Therefore, the purpose of this study is to estimate soil erosion amount and sediment amount according to rainfall-runoff by using rainfall, discharge, and sediment in the Seolmacheon experimental catchment. And, it proposed sediment delivery ratio of the Seolmacheon catchment by result of studying sediment delivery ratio. Hereafter, this study will estimate sediment delivery ratio by basin characteristics, and formulate the method of estimating soil erosion and sediment outflow in various conditions by applying the results in other catchments.

• Journal of Ocean Engineering and Technology
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• v.20 no.2 s.69
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• pp.29-35
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• 2006

The flow patterns around multi-circular cylinders are studies, in order to obtain a global view on the structure of wave control and circulation of sea flow in coastal region. The flow force depends upon the vortex shedding exerted on the structure, especially how the vortex shedding affects the erosion when the structure sets on the sand bottom. Therefore, it is necessary that the flow pattern be hocked. In order to simulate the flow around multi-circular cylinders, the CFX and FLUENT of the computational fluid dynamics (CFD) program were used and compared with the experimental results of the flow visualization installation. The phenomena of flow around the multi-cylinders will be applied to fundamental data for predicting the flow force acting against the structure, erosion and sedimentation around cylinders in arrangement.